In general, stones such as marble and granite are widely used as exterior, interior, or flooring materials in buildings. Such stones are quarried in blocks having a hexahedral shape and are cut into a plurality of slabs.
In the related art, stone cutting devices have been used to cut stone blocks into a plurality of slabs.
Such a stone cutting device includes at least one cutting tool to cut stone, and a frame unit holding the cutting tool and moving the cutting tool relative to the stone for cutting thereof.
Various cutting tools are used according to the shapes or materials of workpieces. For example, a disk-shaped rotating cutting tool may be used to cut a workpiece, or a linear blade-shaped reciprocating cutting tool may be used to cut a workpiece.
An example of a stone cutting device using a linear blade-shaped cutting tool is a frame gang saw.
A frame gang saw, a typical of stone cutting devices of the related art, includes a frame unit and a plurality of blades coupled to the frame unit. While applying tension to each of the blades to maintain the linearity thereof, the frame unit may move in continuously reciprocating motions along the length of a stone block to cut the stone block into slabs.
Such frame gang saws have been widely used for cutting large workpieces such as large blocks of concrete, marble, granite, sandstone, or limestone, into thin slabs.
A common cutting method using a frame gang saw is to cut a workpiece while spraying an abrasive such as granular steel shots onto the frame gang saw.
Recent frame gang saws have included abrasive-containing cutting tips fixed to blades thereof, and techniques for cutting workpieces using such frame gang saws have been developed.
In addition to frame gang saws, other tools such as large circular saw blades, wire saws, or band saws are used for cutting large workpieces.
Large circular saws are disk-shaped, and thus rapid and stable cutting may be guaranteed. Such a large circular saw may include a plurality of blades to simultaneously cut a workpiece into a plurality of slabs. When cutting thick workpieces, a circular saw including large disk-shaped blades may be used. In this case, the thickness of the disk-shaped blades may also have to be increased for the stability of the disk-shaped blades, and thus the size of an overall system may inevitably be increased. This increases the loss of workpieces and manufacturing costs.
In general, wire saws have been widely used for quarrying stones. Recently, wire saws for cutting quarried stone into slabs have been under development. However, processes of cutting stone with a wire saw result in high production costs and a large amount of workpiece loss, and thus applications thereof are limited.
Frame gang saws have been widely used for cutting large blocks of stone without limitations related to the size of workpieces because blades forming the actual cutting parts of frame gang saws can be inserted into workpieces.
Referring to FIGS. 1 to 3B, a cutting tool such as a frame gang saw 10 may include a plurality of blades 12, for example, 250 blades, and each of the blades 12 may have a length of 3 m or more, a thickness of 1.5 mm to 5 mm, and a height of 50 mm to 250 mm.
The frame gang saw 10 may cut a block 1 of granite or marble into slabs, and the slabs may be polished to form finished products such as tiles or blocks. If the thickness deviation of a slab is less than 1.5 mm, the slab is considered to be sufficiently flat. If the thickness deviation of a slab is 2 mm or less, the slab is considered to have an allowable thickness deviation.
When granite or marble is cut using the blades 12, the blades 12 have to be maintained in vertical paths in order to obtain final granite or marble products satisfying the above-mentioned quality requirements.
Referring to FIGS. 3A to 3B, however, when a block 1 is cut with the blades 12, if the blades 12 are twisted or bent because of a force locally applied to the blades 12 in a z-axis direction, the blades 12 may depart from vertical paths (that is, straight paths), and slabs having a thickness deviation outside an allowable range may be produced. In this case, the slabs may be discarded as defective slabs. In addition, due to deformation, the blades 12 may be buckled, broken, worn, or permanently damaged, and thus the effective lifespans of the blades 12 may be shortened.
In a stone cutting device of the related art, tension is applied to both ends of blades of a cutting tool when the cutting tool reciprocates, and thus the stiffness (or linearity) of the blades may be maintained. Furthermore, in the case of a cutting tool using steel shots, blades may be worn by the steel shots, and thus the blades may need to be formed of steel having a high degree of wear resistance. Steel having a high degree of wear resistance may fracture if tension in the steel increases during a cutting process, and thus the degree of tension in the steel is optimally adjusted in consideration of workability. An optimal tensioning force is empirically about 8 tons to 10 tons, though this may vary, according to the kinds of workpieces. In addition, tension has to be uniformly applied to all blades in order to produce slabs satisfying intended dimensions.
Referring to FIG. 4A, in the case of a cutting tool 10 of the related art using steel shots, even in the case that blades 12 depart from their original positions while making contact with a workpiece 1, the blades 12 may easily return to their original positions, for example, by the resilience of the blades 12 because gaps are formed between the blades 12 and the workpiece 1 and thus the blades 12 are not tightly constrained in the workpiece 1. That is, even though a relatively low degree of tension ranging from 8 tons to 10 tons not causing fracturing of the blades 12 may be applied to the blades 12, since the blades are not constrained in the workpiece 1, the blades 12 may not depart from vertical paths during a cutting process.
Referring to FIG. 4B, another exemplary cutting tool 20 of the related art includes cutting tips 24 attached to blades 22.
However, when a workpiece 1 is cut with the cutting tool 20 including the cutting tips 24, the cutting tips 32 are constrained on both sides by the workpiece 1.
In this case, for example, if the cutting tool 20 is impacted and stress is locally formed in the cutting tool 20, the blades 22 may be inclined or bent, and in this state, the blades 22 may cut the workpiece 1.
Therefore, after the workpiece 1 is cut to a certain degree using the inclined or bent blades 22 of the cutting tool 20, since the cutting tips 24 are constrained on both sides by the workpiece 1, the blades 22 may not easily return to their original positions or shapes by the resilience of the blades 22. Therefore, cutting of the workpiece 1 may be continued in a state in which the cutting tips 24 are inclined and constrained by the workpiece 1, and thus the degree of cutting error may increase. That is, if the blades 22 to which the cutting tips 24 are attached are used, stone may be cut at a relatively high speed when compared to a conventional method of cutting stone using an abrasive such as steel shot. However, the blades 22 may easily depart from their positions if tension is applied to the blades 22 within the same range as in the conventional method.
Since the blades 22 of the cutting tool 20 to which the cutting tips 24 are attached are not directly brought into contact with the workpiece 1, the blades 22 may not be worn during a cutting process. Therefore, the wear resistance of the blades 22 may not be a matter of concern, and thus the blades 22 may be formed of high-strength steel resistant to a high degree of tension without fracturing.
Frame gang saws may be broadly classified into two types according to the structure of moving blades of a cutting tool.
One is a type of saw having reciprocating blades in sawing motion, and this type of saw is commonly used to cut stone such as marble.
The other is a type of saw having reciprocally swinging blades, and this type of saw is commonly used to cut stone such as granite, which is harder than marble.
In the case of a sawing-motion reciprocating-type frame gang saw, cutting tips of a cutting tool are continuously in contact with a workpiece during a cutting process. However, in the case of a swing type frame gang saw, blades contact a workpiece about 150 times per minute during a cutting process, and thus the blades may be deformed by impacts.
Therefore, when a swinging type frame gang saw is used to cut a workpiece such as a granite workpiece, blades of the swinging type frame gang saw may be significantly impacted because of the swinging motion thereof, and if cutting tips are attached to lower portions of the blades of the swinging type frame gang saw, the blades may be markedly deformed because the lower portions of the blades are constrained in the workpiece. Therefore, the swing type frame gang saw may require a higher degree of tension than the sawing-motion reciprocating-type frame gang saw or a steel-shot type frame gang saw.
Furthermore, in the case of the above-described cutting tools 10 and 20 of the related art, spacers are used to maintain the shapes of the blades 11 and 22 and gaps between the blades 11 and 22.
Spacers 30 used in a general cutting tool 10 will be described in detail with reference to FIG. 5. In the related art, the spacers 30 are disposed between blades 12 and engaged with the blades 12.
In this case, left and right sides of the blades 12 are constrained by the spacers 30 (in a y-axis direction), and thus tension in the blades 12 is not uniform. That is, since the blades 12 are moved in a state in which the blades 12 are constrained by the spacers 30, tension may not be smoothly applied to the blades 12. That is, tension applied to both ends of the blades 12 may not be properly distributed in the blades 12, and thus the amount of tension in the blades 12 disposed between the spacers 30 may be less than a required amount.
As described above, tension in the blades 12 of the related art may not be properly maintained according to the wear states or required durability of the blades 12. In this case, the durability of the cutting tool 10 and the cutting quality of workpieces may be decreased. Thus, it is required to solve these problems.
A representative related technique is disclosed in Korean Patent No.: 10-1072382 (Oct. 5, 2011).